Passengers could also face pricier tickets if the jobs go, the Transport Salaried Staffs Association (TSSA) said.
It said 100 jobs were set to be axed at 12 travel centres on Virgin’s East Coast line between London and Edinburgh.
Across Yorkshire, it runs travel centres at stations in York, Wakefield and Doncaster, plus a travel centre in the First Class lounge at Leeds.
Ticket office staff would be moved out of officers and onto platforms to sell tickets from hand-held machines.
A TSSA spokesman said around 40 people currently work at the four Yorkshire sites. A third of the roles are expected to be axed, he added.
Virgin’s plans follow union action in the capital over Govia Thameslink Railway’s plans to close more than 80 ticket offices and move staff on to station concourses. They are also still campaigning against the closure of ticket offices on London Underground.
TSSA leader Manuel Cortes said: “This is another example of passengers finding a service is being cut in the name of private profit.
“Virgin wants to move ticket office staff out on to ‘customer service zones’ on platforms where they will sell tickets from hand-held machines.
“Passengers will be faced with a narrower range of the cheaper tickets because hand-held machines do not offer a full service.
“This will be a recipe for travel chaos when platforms are at their busiest during peak travel times.
“We should go back to the publicly-run East Coast Main Line franchise which was a non profit-making line where passenger service was paramount. The sooner all railways are taken back into public ownership the better.”
A Virgin Trains spokesman said: “We’re investing heavily in the East Coast franchise and have made a number of changes already, such as new interiors on our trains, and have seen our customer satisfaction scores rise as a result.
“At Virgin Trains we are always looking for ways to improve things further for our customers, who are at the heart of every decision we make. Of course where any of these changes affect our people we’ll consult fully with them and their representatives.”